Shooting incidents in the U.S. and in the rest of the world are on the rise. The number one problem most police personnel and U.S. forces operating in hostile urban areas face is not being able to detect where the shooter is actually located at any given time during the pursuit. It is difficult for humans to rely strictly on their hearing to locate where the sound of gunfire is coming from. Police and military personnel also have trouble relying on witness accounts during these events because people often give inaccurate information when they are in a state of panic, shock and confusion. Additionally, decisions must be made very quickly and accurately before additional causalities are inflicted. A solution that would greatly benefit military, police and law enforcement agencies should offer not only real-time detection of transient sounds such as gunshots or explosives, but also the ability to determine the location of sources of the transient sounds.
Guns, including firearms and artillery, generally generate a muzzle blast when the gun is fired. The muzzle blast propagates spherically outwardly from the muzzle of the gun. Some prior known systems use only the muzzle blast to attempt to locate the origin of the gunshot. Such systems can use acoustic sensors and triangulation methods to find the origin of the gunshot. Other systems that use only the muzzle blast for locating the origin of the gunshot, record the Time of Arrival (ToA) of the wavefront of the muzzle blast at a plurality of sensors in known locations. These systems can perform trilateration or multilateration using the ToA or the Time Difference of Arrival (TDoA) of the acoustic wavefront of the muzzle blast at the sensors to locate the origin of the gunshot.
There are several known problems with systems and methods that use only the muzzle blast to find the location of a gunshot. The muzzle blast can be suppressed. Buildings and local topography can corrupt the acoustic signal of the muzzle blast. Multipath signals or echoes can obscure the original muzzle blast acoustic signal.
Projectiles fired from some guns exceed the speed of sound. These supersonic projectiles generate a ballistic shock wave. This shock wave is an acoustic pressure wave signal that propagates from the projectile, normal to the shock wave cone 33, as the projectile travels.
Prior known systems that use only the shock wave to compute the trajectory of the projectile generally require a directional array of sensors. The ability to find the origin of the gunshot using only the shock wave is limited. U.S. Pat. No. 5,241,518 to McNelis, et al. discloses a system and method with three precisely located sensors each having three closely spaced, precisely positioned transducers. The method in McNelis, et al. uses the ToA of the shock wave at each transducer in a sensor to compute an angle of arrival, and computes a trajectory from the three angles of arrival. The method in McNelis, et al. assumes the shock wave is a plane wave and a constant velocity projectile.
U.S. Pat. No. 7,292,501 to Barger discloses a system and method that uses force sensors to compute the angle of arrival of the shock wave, and therefrom, the trajectory of the projectile. U.S. Pat. No. 7,126,877 to Barger, et al. discloses a system and method that uses an antenna with a spherical array of seven sensors to detect a projectile shock wave cone 33 and compute the projectile trajectory.
Other prior known systems and method use both the muzzle blast and shock wave to locate the origin of a gunshot. U.S. Pat. No. 7,359,285 to Barger, et al. discloses a system and method that uses an antenna similar to that used in the '877 patent, and further uses the muzzle blast to calculate the origin of a gunshot. U.S. Pat. No. 6,178,141 to Duckworth et al. discloses a system and method that utilize the shock wave to calculate the projectile trajectory and the muzzle blast to locate the origin of a gunshot. Duckworth et al. discloses using at least six distributed individual microphone nodes or at least two nodes with three microphones each. In Duckworth et al. the caliber of the projectile is first estimated, and a ballistic coefficient and thereby the deceleration are then estimated based on the caliber estimate. The ToAs or TDoAs from the nodes are then used to calculate the projectile trajectory.
Systems and methods that use several closely spaced sensors may be placed in a disadvantaged location and receive only reflected and/or corrupted signals. A distributed network of sensors is more likely to receive clean, direct acoustic signals at enough nodes to reliably calculate the origin and trajectory of a gunshot projectile. Additionally, array-based systems and methods require precise orientation of the sensor array in order to find the angle of arrival of the shock wave. The array-based systems and methods require proper calibration in order to provide an accurate angle of arrival. Prior known systems and methods that use distributed sensor networks do little processing at each node and transmit entire waveforms to a base station for processing. Limited wireless bandwidth in such systems limits the number of nodes and slows transmission of data to the base station, which prevents real-time location finding of the shooter.